Maximum Comfort Efficiency? Evolution Sys

[skidder]

Summer is back. Therefore I was thinking about the settings on the Evolution system. FWIW, I'm very happy with this Bryant system. Very comfortable all winter.

To the point. The control has 3 settings for AC Airflow: Maximum, Comfort, Efficiency.

I'm going to pull out the manual later - but any hints. I've had it on Comfort the whole time.

I have a MAA315 Evolution 80, York 2 Ton, ADP 3 ton with TXV (approved for 2,2.5,3 ton flow).

I keep wanting to set the outdoor unit as a 2.5ton. It just seems that the airflow is so low with 700CFM (2 ton). Especially when this thing kicks into Dehum - 450CFM! Tiny. I have no idea how this thing will keep up on a 100 degree day as I've put in R-49 (had R-22 if that) insulation in the attic in the fall - so who knows what I'll get this summer. When I purchased the system I cacled it around a R-49 house and sized it right. The old system I took out was a giant 3.5 Ton Trane from the Mid-80s.

I get hung up on this CFM boost more than anything. I want to set it at 875. The coil is big enough, the York is rated at 400CFM/ton or 800CFM. So that doesn't seem like a bad idea. In some way I think I'd get 'higher' efficiency because the condenser would run less time. My concern is I'll jack the humidity control, increase static pressure and just defeat the purpose of comfort.

Any thoughts on the AC Airflow setting and putting the thing as a 2.5 or a 2.0 Ton?

Thanks.

[beenthere]

Set it for 2 tons, and leave it on comfort.

If it doesn't handle the load, then set for eff.

[dash]

I'd leave it on comfort,unless you are in a dry climate.

If you want,leave it on two tons,and set it for effiecency,and try it.

Considering you had a 3.5 ton,the air flow is a lot less now,also doubtful that static would be a problem if you set the air flow higher.

[skidder]

Ok - thanks for the advice. I'll leave it at 2 and Comfort. Does efficiency just raise the CFM?

[dash]

The cfm will be raised,which does increase the SEER,over the Comfort setting,may want to try it if you are in a dry climte.I'm in Florida,so comfort setting is the best here.

[wyounger]

If you're in a humid climate, you should probably stick with Comfort. If you're in a dry climate, Efficiency will do fine, and Maximum might be ok for full-on desert locations. You have experienced dehumidification activity, though, which suggests to me that you're not in the desert.

From what I've seen the only difference between Comfort and Efficiency has more to do with the fan-off delay after a cooling cycle than fan speed itself. I've had mine set both ways and it usually runs 350 cfm/ton either way. Comfort seems to turn off the indoor fan immediately when the compressor stops, and efficiency will run for awhile to take advantage of the cold mass in the indoor coil before it stops (provided there isn't demand for much dehumidification). My system has actually controlled humidity fine for me so far this year while set on Efficiency, despite being in Atlanta and having a single-speed outdoor unit. I used Comfort last year, and am going to stick with Efficiency this year to see how much difference I can find.

If the system is having trouble maintaining the set temperature, it can go to higher cfm/ton rates even if it's set to Comfort. When my Infinity system was first started up, the house had gotten up into the high 80s (this was a mid-summer install). It was set for Comfort, but it started up at 400 cfm/ton because it was so far from the setpoint. As it got closer to the temp setpoint, it backed off to 350 cfm/ton so it could dehumidify enough to satisfy the RH setpoint too. I haven't seen 400 cfm/ton since, but we haven't had any unusually hot summer days in the 10 months I've had the system.

I don't recommend changing your airflow settings to 2.5 tons. You may be surprised at how well it keeps up when it does get hot. Of course it's going to run a lot in hot weather- that's the whole point of sizing it correctly. It should run almost around the clock in the hottest summer weather. Provided the load calc is correct, it's going to do fine.

And don't worry about it trying to run 450 cfm when it's 100 outside, either; that mode is really only for use when there is demand for dehumidification without any need for cooling. Higher CFM settings are going to ruin your ability to dehumidify, especially with an ADP 3-ton coil.

[seadragon]

wyounger,

Great post!

This is going to be our first cooling season with the Infinity control so I am very interested to hear details like you posted on how the different modes work. I was wondering what the diff was between Comfort and Efficiency and now know the answer.

Thanks again!

Ken

[skidder]

wyounger - thanks for that information. That was exactly the routine I was going to go thru myself. That information saves me a lot of work.

I'm in relatively dry MN. I also have a 70 pint dehum running set to 45% in the basement laundry room (~700sq ft). The Laundry area isn't heated or cooled - the other 1/2 of the basement (~900 sq ft) is heated and cooled with intake and exhaust ducts. The dehum takes the moisture out of most of the basement reguardless of the walls between the rooms. That effectively keeps the whole house humidity down.

I've been running the stat in Efficiecny since your post. It seems to do exactly what you said. It isn't HOT yet but - it seems to do fine in Eff. I'll keep an eye on it.

I've also definately decided to stay with 2.0. A lot of engineering went into this stat; why give it the wrong inputs for the equipment. I've got to let go and let it do it's job! Leaving the hood down on things has always been my weekness.

Thanks for the informational post.

[wyounger]

Leaving the hood down? Nah, I can't either. But I don't stress myself out about what I may see. I just enjoy watching genius at work.

I hit 56% RH briefly this weekend, which gave me the nudge to override the cooling setpoint from 76 to 75 for a couple of hours, and I set the thing back to Comfort.

Then after the setpoint had expired, I got all hot and bothered (having just gotten back from the gym) and set another override to 75. It had whooped all that humidity by then, but by that point it was nearly 90 outside and knew that it was going to have to really work to pull down a full degree in the middle of the heat of the day. A few minutes later, I noticed my discharge temp was a few degrees higher than normal. But what, me worry? Nope. I checked and found that it had stepped up to 375 cfm/ton, despite being in Comfort, because it really needed the sensible (temperature) cooling more than the latent (humidity removal). Awhile later, it had achieved that one degree and went back to 350 cfm/ton to keep humidity in line.

At another point this weekend, it started up just to dehumidify... I saw it run 215cfm/ton for the first few minutes of the cycle, then step up to... 315, I think it was. Yesterday was one of those Georgia days where it rains for a few minutes, then the sun comes out and makes all the surfaces steam for a few minutes, and then it repeats the cycle. Hooray for humidity control; without it I'd still be in California, I think

Maybe there's more difference between Efficiency and Comfort than is obvious, but it's not so simple as that one is 350 and the other is 400. Both will apparently do both, depending on what conditions demand, so I guess the difference must be more in how it decides when to use what flow rate.